V.42

Definition - What does V.42 mean?

V.42 is an International Telephone and Telegraph Consultative Committee (CCITT) V-series standard that regulates error-detection for high-speed modems. V.42 permits computer modems to work with both digital and analog phone lines. It’s an error-correcting procedure for data communications equipment (DCE) that uses an asynchronous-to-synchronous conversion.

V.42 is pronounced as v-dot-forty-two.

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Techopedia explains V.42

V.42 permits receivers to request the retransmission of lost data packets, although it does not provide a guarantee about how much time it will take to deliver the error-free data to the receiving side. V.42 is generally included in dial-up modems and even includes an high-level data link control-based protocol referred to as Link Access Procedure for Modems.

The V.42 protocol includes some well-defined characteristics:

A non-error-correcting mode with V-series DCE, including asynchronous-to-synchronous conversion according to ITU Telecommunications Standardization Sector recommendations
Permits error detection using a cyclic redundancy check. Error correction is performed using the automatic retransmission of data.
Enables synchronous transmission through start-stop data conversion and an initial handshake in start-stop format that minimize DTE disruption